“分段”和“分类”是两种不同的逻辑划分.分段是对主元的取值进行划分,所讨论的式子不因分段而改变;而分类是对客元的取值进行划分,所讨论的式子会随之变化.分段讨论后的结果取并集或交集,分类讨论后的结果取并集或分类叙述.下面举例说明. “Segmentation” and “classification” are two different logical divisions. The segmentation is the division of the value of the pivotal element, the formulae discussed are not changed by the segmentation, and the classification is performed on the value of the guest element. Division, the formula discussed will change with it. The results after segmentation take unions or intersections, and the results of the classification discussion take the union or classification description. The following examples illustrate.